With progress of electric power industry, electric appliance industry, electromechanical products are developing towards miniaturization, high accuracy and high efficiency. Iron cores made of ordinary cold-rolled silicon steel sheet are hard to meet various requirements. Accordingly, it is an important approach to develop a series of efficient non-oriented electric steel products of low-iron-loss, high-magnetic-induction to take the place of ordinary cold-rolled silicon steel sheet, so as to reduce volume, reduce weight, and save steel and copper consumption, and improve efficiency for electromechanical products.
Main magnetic feature of high-efficiency non-oriented silicon steel lies in high magnetic induction. The features of its conventional manufacture process lie in that: after being hot-rolled, the hot-rolled plates are normalized to homogenize texture of the hot-rolled plates increase re-crystallized grains, prevent corrugation-shaped defects, and meanwhile to make grains and separated substances more coarse, intensify components (110) and (100), decrease component (111) and thus improve magnetic property significantly. In order to enhance magnetic induction, normalization temperature is usually over 950° C. However, the normalization of hot-rolled plates brings problems of high manufacture cost and long manufacturing cycle.
Chinese patent CN1288070 discloses a non-oriented silicon steel, compositions of which are: C≦0.008%, Si 0.2-2.50%, Mn 0.15-0.8%, Als residual volume˜1.50%, B residual volume˜0.0035%, P+Sn/Sb 0.08-0.45%, S≦0.003%, N≦0.003%, the rest being Fe and unavoidable impurities. Iron cores of high-efficiency electric machine are manufactured by processes of low temperature hot-rolling, single cold-rolling and dry gas or moisture annealing.
Japanese patent publication 2004-169141 refers to normalization-exemption production of hot-rolled plate of high grade steel with compositions 1.8%≦(Si+2Al)≦5%, which requires that one or two among REM, Mg and Ca should be added during steelmaking, and meanwhile Ti content should be strictly controlled Ti≦0.003%; during hot-rolling, it is required to finish-roll at 950° C. or more, and reel at 700° C. or less. The shortcomings of this production lie in rigorous hot-rolling process conditions, high finish-rolling temperature and difficulties in actual production operation and control.
Patents about annealing-exemption process for hot-rolled plates further involve Japanese patent publication 2008-260980, which requires that composition system of the steel therein belongs to steel group of high Si content that requires Si content between 1.5%-3.5%, (% Si+% Al)≧1.9%; at the time of hot-rolling, heating temperature for slab is high, being 1230-1320° C.; finish-rolling temperature is at 1050° C. or more, and reeling temperature is at 700° C. or less. The shortcomings of this process lie in hot-rolling temperature for slab of the hot-rolled plate being too high, and MnS and AlN being prone to thinly disperse and separate out during hot-rolling process to deteriorate magnetic property, and to make surface scale hard for removal.